U.S. Pat. No. 6,169,198 describes the process of hydrocyanation (reaction with HCN) of butadiene (BD) to prepare adiponitrile (ADN), and explains that the process can generally be divided into three steps. First, mononitriles such as 3-pentenenitrile (3-PN) are formed by the reaction of HCN with BD, along with other nitriles, including isomers which must be isomerized in subsequent steps to achieve the desired straight chain ADN as a final product. Second is the isomerization of species such as 2-methyl-3-butenenitrile (2M3BN). Third is a second hydrocyanation of the pentenenitriles to yield the desired ADN.
U.S. Pat. No. 5,981,722 describes and exemplifies a new class of catalysts for such transformations by the use of diphosphite nickel complexes for the hydrocyanation and isomerizations. This class of catalysts is characterized by greater catalytic activity and resistance to HCN-derived degradation reactions.
U.S. Pat. No. 7,470,805 describes a process of hydrocyanation of diolefins in the presence of a catalytic system comprising a transition metal and mono- and pluri-dentate organophosphorus ligands. According to this, the use of a mixture of two ligands, monodentate and pluri (bi and/or tri)dentate, enables the pluridentate ligand to be preserved in the reaction milieu.
Monodentate and bidentate phosphorus-based ligands, depicted as formulae (7) and (8), and (3), respectively, as the structures are termed in U.S. Pat. No. 7,629,484, can be used in preparation of a transition metal-organophosphorus catalyst for reactions such as hydrocyanation.